When I have to debug some web application I often stared at the Apache log and say WTF!!
This is what the log might looks like:

The problem comes because every time I go into the web I get hundreds of unrelated log lines, a huge mess!

So one day I thought, could I improve that? My first idea was to add some color using grep like this:

tail -f /var/log/apache2/error.log | grep -E "ERROR|" --color

That is nicer because now I can see clearly errors in red.
Could that be better? Maybe yellow warnings?
The answer is yes, grep output can be concatenated to another grep and different colors can be used in every grep. Like this little script: